Several aspects of phagocyte biology have been studied using neutrophils (PMN) and monocytes. Investigation of the subcellular location of fmet-leu-phe, C3bi as well as for cytochrome b suggests these constituents are packaged in a common compartment similar to specific granules. In related studies a series of monoclonal antibodies against the inside of the neutrophil plasma membrane have been developed with the goal of identifying specific secretory granule attachment sites. Studies in exudate PMN have revealed greater than five-fold more fmet-leu-phe receptors than blood PMN, presumably related to receptors mobilized from the intracellular pool. In studies extending our earlier work on neutrophil heterogeneity a monoclonal antibody, 31D8, that binds to a subpopulation of PMN was studied in chronic myelogenous leukemia (CML). The data indicate there are two groups of CML patients; those with 31D8 bright or dull PMN. It is not clear whether or not the CML heterogeneity reflects differences in clonal proliferation. Unexpectedly absence of the 31D8 antigen appeared predictive of progression of CML to the accelerated phase. Studies of IgE turnover in the Hyperimmunoglobulin E-recurrent infection (Job's) syndrome have revealed decreased clearance of IgE in subjects with elevated IgE. This has implications for numerous diseases in which IgE is elevated. In other studies gamma interferon was shown to be a chemoattractant for PMN and monocytes and this may relate to gamma interferon's ability to induce macrophage giant cell formation.